The products of fermentation are usually found in complex mixtures of dilute solutions and must be concentrated and purified. The separation of the product of interest from the fermentation broth depends on the accumulation of the product, which may be intracellular or extracellular. The typical downstream operations and the unit operations involved in the processing of fermentation broth (148) are:
1. Cell separation (settling, centrifugation, dead end filtration, and cross flow filtration)
2. Cell disruption (high pressure homogenization, wet milling, and lysis)
3. Clarification of extract (centrifugation, extraction, dead end filtration, and cross flow filtration)
4. Enrichment (precipitation, batch adsorption, ultrafiltration, and partition)
5. High resolution techniques (ion exchange, affinity, hydrophobic, gelfiltration, adsorption chromatography, and electrophoresis)
6. Concentration (sterile filtration, diafiltration, ultrafiltration, freeze drying, spray drying, and precipitation).
While downstream processing is an important part of fermentation process development, a detailed discussion on the subject is outside the scope of the chapter and hence not dealt with.
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